The present disclosure generally relates to a system and method for depressurizing a molecular sieve. More specifically, the present disclosure relates to a method and system that utilizes a low pressure eductor type vapor condenser in the recycle stream from the molecular sieve.
Ethanol production has been the largest single application of corn processing since 1999, reflecting the recent high growth of the fuel ethanol market as an alternative fuel to gasoline. Ethanol is typically produced from corn through either a wet or dry milling process. In the wet milling process, the corn kernel is separated into its components including germ, fiber, protein and starch.
In a dry mill process, whole corn is ground into flour, treated with enzymes, chemically modified and cooked. The resulting “mash” is treated with enzymes to further break down the starchy endosperm tissue into glucose. The converted mash is fermented and distilled, producing ethanol, carbon dioxide, and distiller's grains with solubles (“DDG”).
Within typical ethanol production facilities, a small percentage of water, typically 5% by volume, is present in the ethanol resulting in 190-proof ethanol. Current technology for ethanol production employs molecular sieves to remove the last approximately 5% of water from the product. A molecular sieve is typically a bottle containing ceramic beads or other media with an affinity for water. When the 190-proof ethanol passes through a molecular sieve, the molecular sieve pulls the last approximately 5% of water resulting in anhydrous ethanol, i.e. 200-proof, that can be blended with gasoline.
The process typically will heat 190-proof ethanol liquid in a heat-exchanger, called an economizer, and then pass the heated liquid into a vaporizer, which converts the liquid to vapor, which is then fed into one or more molecular sieves at a much higher pressure to produce 200-proof ethanol. However, after a sieve bottle is in production for a period of time, the media within the sieve becomes saturated and may start passing ethanol containing more moisture than is desired. At this point, the molecular sieve will be taken off line and put under deep vacuum conditions to regenerate the molecular sieve. The regeneration steps consist of a depressurization cycle and a deep vacuum cycle. Typically, the molecular sieve is depressurized back to the 190-proof condenser from the feed side of the bottle. This is referred to as reverse flow. The reverse flow stream then passes to the surge tank and is then pumped back as a reflux flow to the rectifier or back to the 190-proof storage tank to begin the process again through the economizer and vaporizer as a recycle stream, which will use additional energy before it is transformed into anhydrous ethanol.
Reverse flow systems for regenerating molecular sieves reduce plant capacity and consume additional energy. Because there is a large number of existing ethanol plants based on corn dry milling, and the number is increasing rapidly, it would be desirable to have a process that could be integrated into these plants to improve plant effectiveness and increase capacity with the least energy consumption. Further, steady flow conditions will minimize the negative effect of fusel release into the ethanol discharge.